Air-gap type FBAR, and duplexer using the FBAR

ABSTRACT

An air-gap type film bulk acoustic resonator (FBAR) is created by securing two substrate parts, one providing a resonance structure and the other providing a separation structure, i.e., a cavity. When the two substrate parts are secured, the resonance structure is over the cavity, forming an air gap isolating the resonant structure from the support substrate. The FBAR may be used to form a duplexer, which includes a plurality of resonance structures, a corresponding plurality of cavities, and an isolation part formed between the cavities. The separate creation of the resonance structures and the cavities both simplifies processing and allows additional elements to be readily integrated in the cavities.

CROSS REFERENCE TO RELATED APPLICATION

This is a divisional application based on application Ser. No.10/825,608, now U.S. Pat. No. 7,053,730, filed Apr. 16, 2004, the entirecontents of which is hereby incorporated by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to a film bulk acoustic resonator (FBAR)and a duplexer using the FBAR. More particularly, the present inventionis directed to an air-gap type FBAR and a duplexer fabricated through asimple substrate-securing process, and fabricating methods thereof.

2. Description of the Related Art

As mobile communication devices, such as cellular telephones, becomeincreasingly prevalent, demand for compact, lightweight filters used insuch devices is also rising. Film bulk acoustic resonators (FBARs) canbe used as such compact, lightweight filters and can be inexpensivelymass-produced. Also, the FBAR can obtain a high quality factor (Q)value, can be used in a micro-frequency band, and, more particularly,can be implemented up to PCS (Personal Communication System) and DCS(Digital Cordless System) bands.

Generally, the FBAR is implemented by laminating a first electrode, apiezoelectric layer, and a second electrode on a substrate in thatorder. In operation, an electric field, which varies with time, isinduced in the piezoelectric layer by applying electric energy to theelectrodes. This electric field causes a bulk acoustic wave to begenerated in a vibrating direction of the piezoelectric layer, therebygenerating resonance.

FIGS. 1A to 1C illustrate cross-sections of a Bragg reflector type FBAR,a bulk micro-machining type FBAR, and a surface micro-machining typeFBAR, respectively. Each of these types of FBARs provides separationbetween the substrate and the multi-layer resonance section in differentmanners. The separation is needed so that acoustic waves generated fromthe piezoelectric layer are not affected by the substrate.

The Bragg reflector type FBAR in FIG. 1A includes a substrate 10, areflector structure 11, a lower electrode 12, a piezoelectric layer 13,and an upper electrode 14 in that order. The reflector structure 11includes a plurality of dielectric layers alternating between lowimpedance and high impedance materials to insure efficient confinementof the acoustic energy in the resonator. Thus, elastic-wave energy,which has passed through the piezoelectric layer, is not transferred tothe substrate 10, but is wholly reflected by the reflector structure 11to generate an efficient resonance. The Bragg reflector type FBAR isrobust and is subject to no bending stresses. However, precise thicknesscontrol of the layers of the reflection structure 11 for the totalreflection in such a Bragg reflector type FBAR is not easy and increasesthe manufacturing cost.

The bulk micro-machining type FBAR in FIG. 1B includes a membrane 21 ofa material, such as SiO₂, on a substrate 20, a cavity 23, formed byanisotropic-etching the rear surface of the substrate 20, and anacoustic resonator 22 on the membrane. Again, the acoustic resonator 22includes a lower electrode, a piezoelectric layer and an upperelectrode. The bulk micro-machining type FBAR is very weak structurally,making its implementation impractical.

The surface micro-machining type FBAR in FIG. 1C includes a substrate30, an air gap 31, a dielectric layer 32, and a first electrode 33, apiezoelectric layer 34 and a second electrode 35 on the dielectric layer32 in sequential order. This FBAR is fabricated using a sacrificiallayer on the substrate 30 and forming the dielectric layer 32, on thesacrificial layer, forming the resonator structure on the dielectriclayer 32, and then removing the sacrificial layer to form the air gap31. That is, the air gap 31 is formed in a position where thesacrificial layer existed. The surface micro-machining type FBAR, has acomplicated fabricating process and the resonance structure may cave inor peel off during the fabricating process.

Also, the above conventional FBARs have the common problem in thatseparate packaging, which requires lots of time and expense, is neededafter the FBAR has been fabricated, and the FBAR may be damaged due toheat generated during the packaging process.

A duplexer is a representative element that uses multiple filters. Theduplexer properly branches signals transmitted/received through oneantenna in a frequency division type communication system so that thesame antenna can efficiently both transmit and receive. The duplexerbasically includes a transmitter filter and a receiver filter inaddition to an antenna. The transmitter filter is a band pass filter forpassing only a frequency to be transmitted, and the receiver filter is aband pass filter for passing only a frequency to be received. Theduplexer can perform the signal transmission/reception through oneantenna by adjusting the frequencies passing through the transmitterfilter and the receiver filter. The duplexer can improve its performanceusing the FBAR as its transmitting/receiving filter.

Since the difference between the frequencies of the signalstransmitted/received through the transmitter filter and the receiverfilter is small, the signals influence each other giving rise tointerference. Accordingly, an isolation part that isolates thetransmitter filter and the receiver filter from each other to preventmutual interference may be incorporated in the duplexer to improveperformance. The isolation part includes a phase shifter using acapacitor and a resistor, and prevents the mutual interference byintroducing a phase difference of 90° between the frequencies of thetransmitted signal and the received signal.

The duplexer in FIG. 2A includes a transmitter filter 41, a receiverfilter 42, and an isolation part 43 for isolating the two filters fromeach other on a printed circuit board (PCB) 40. The transmitter filter41 and the receiver filter 42 are wire bonded to the PCB 40, creating ahybrid design. This duplexer can be fabricated using the air-gap typeFBAR as shown in FIGS. 1B and 1C. However, the separate packaging foreach FBAR increases the size of the duplexer, reducing the usefulness ofthe duplexer in miniaturized devices. Also, losses due to the wirebonding may occur.

FIG. 2B shows a duplexer fabricated on one substrate 50 using the Braggtype FBAR of FIG. 1A. Only details of a representative FBAR 60 will bediscussed below. The FBAR 60 includes a reflector layer 64 formed byalternating layers of materials having greatly different acousticimpedances, a lower electrode 63, a piezoelectric layer 62, and an upperelectrode 61 in that order, as a filter. As shown in FIG. 2B, thereceiver filter includes a serial resonator 60 and a parallel resonator70, and the transmitter filter includes a serial resonator 80 and aparallel resonator 90, all of which are integrated onto one substrate50. The Bragg type duplexer is fabricated on one substrate to effect aone-chip fabrication. The Bragg type duplexer has a strong structure,but it is difficult to accurately adjust the width of the respectivelayers, and the thin film is easily cracked due to the stress causedduring formation of the thick reflector layer. Further, the Bragg typeduplexer has a greatly lowered Q value compared to a duplexer using anair gap type FBAR.

SUMMARY

The present invention is therefore directed to an air gap type film bulkacoustic resonator (FBAR), a duplexer including the FBAR, and amanufacturing method for both, which substantially overcome one or moreof the problems due to the limitations and disadvantages of the relatedart.

It is a feature of the present invention to provide a robust, simplyfabricated air-gap type FBAR. It is another feature of the presentinvention is to provide to a duplexer including a robust, simplyfabricated air-gap type FBAR and an isolation part, and a fabricatingmethod thereof. It is yet another feature of the present invention tocreate such a robust, simply fabricated FBAR using a substrate securingprocess.

At least one of the above and other features may be realized byproviding an air-gap type FBAR including a substrate having a cavity inan upper surface of the substrate, a first dielectric layer on the uppersurface of the substrate around the cavity, a resonance part, and asecond dielectric layer formed on the resonance part. The resonance partmay include a first electrode on part of the first dielectric layer, asecond electrode on the first dielectric layer, exclusive of the firstelectrode, and a piezoelectric layer between the first and secondelectrodes. The FBAR may include a via exposing a pad for providingelectrical contact with the first and second electrodes.

A conductive layer may be provided on a bottom surface of the cavity. Apassive and/or active element may be integrated on a bottom surface ofthe cavity. A substrate film of a predetermined thickness may be on thesecond dielectric layer. The FBAR may further include a third dielectriclayer on a portion of a surface of the substrate film and a secondsubstrate contacting the third dielectric layer, the second substrateincluding a cavity formed apart from where the second substrate contactsthe third dielectric layer.

At least one of the above and other features may be realized byproviding a method of fabricating an air-gap type FBAR including forminga resonance part on a first substrate, forming a cavity in a secondsubstrate, securing the first substrate with the second substrate sothat the resonance part is located in the cavity, and packaging byremoving at least part of the first substrate after the securing. Theforming of the resonance part may include sequentially providing a firstdielectric layer, a first electrode, a piezoelectric layer, and a secondelectrode on the first substrate. A pad may be formed by exposing partof the first and second electrodes by removing corresponding portions ofthe first dielectric layer part of the resonance part.

The forming of the resonant part may further include depositing thefirst dielectric layer on the first substrate, selectively depositingthe first electrode on the first dielectric layer, selectivelydepositing the piezoelectric layer on the first electrode and the firstdielectric layer, and selectively depositing the second electrode on thefirst electrode, the first dielectric layer and the piezoelectric layer.

The forming of the cavity may include depositing a second dielectriclayer on the second substrate, exposing part of the second substratesurface by removing part of the second dielectric layer, and etching theexposed part of the second substrate to form the cavity. The securing ofthe first and second substrates may include bringing the first substrateand the second dielectric layer on the second substrate into contact.

A conductive layer may be selectively deposited on a bottom surface ofthe cavity before the securing. An active and/or passive element may beintegrated on a bottom surface of the cavity before the securing. Aresonance frequency of the FBAR may be tuned by controlling a thicknessof the first dielectric layer in the resonance part. The securing mayinclude bonding using adhesive bonding and/or eutectic bonding. Thepackaging may include etching the first substrate to a predeterminedthickness or completely removing the first substrate. The packaging mayinclude selectively depositing a third dielectric layer on a thirdsubstrate leaving an exposed part of the third substrate surface,forming another cavity by etching the exposed part of the thirdsubstrate, and securing the third substrate with the first substrate atthe third dielectric layer.

At least one of the above and other features may be realized byproviding a single-chip duplexer having a FBAR filter including asubstrate having first and second cavities formed on an upper surface ofthe substrate, a first dielectric layer deposited on the upper surfaceof the substrate around the first and second cavities, a first air-gaptype FBAR including a first resonance part over the first cavity, asecond air-gap type FBAR including a second resonance part over thesecond cavity, and an isolation part between the first air-gap type FBARand the second air-gap type FBAR.

Each resonance parts may include a lower electrode on an upper surfaceof the first dielectric layer on one side of a cavity and extending overthe cavity, an upper electrode on the upper surface of the firstdielectric layer on an opposite side of the cavity and extending overthe cavity, and a piezoelectric layer formed between the lower electrodeand the upper electrode over the cavity.

One of the first and second air-gap type FBARs may act as a transmitterfilter, and the other may act as a receiver filter. The transmitterfilter and the receiver filter may be implemented by connecting morethan one air-gap type FBARs.

The isolation part may include a capacitor and a resistor, and introducea phase difference between frequencies of signals input to thetransmitter filter and the receiver filter. The isolation part mayinclude a second dielectric layer on the substrate, a first conductivelayer on part of the upper surface of the second dielectric layer, athird dielectric layer on part of the first conductive layer and on partof the upper surface of the second dielectric layer, a second conductivelayer on part of the third dielectric layer over the first conductivelayer and on part of the third dielectric layer below which the firstconductive layer is not present, an insulating film on part of thesecond conductive layer and on an upper part of the third dielectriclayer, and a conductive coil on an upper part of the insulating film andon upper parts of exposed first and second conductive layers.

At least one of the above and other features may be realized byproviding a method of fabricating a single-chip duplexer using anair-gap type FBAR filter, including forming a first substrate parthaving first and second resonance parts formed at predeterminedintervals on a surface of a first substrate, forming a second substratepart including forming first and second cavities at the predeterminedintervals on a second substrate and forming an isolation part betweenthe first and second cavities, securing the first substrate part and thesecond substrate part so that the isolation part is located between thefirst and second resonance parts and the first and second resonanceparts are over the first and second cavities, respectively, and removingthe first substrate of the first substrate part after the securing.

The forming of the first substrate part may include selectivelydepositing a first dielectric layer on the first substrate to form firstand second dielectric portions for the first and second resonance parts,respectively, depositing first and second lower electrodes on part ofthe first and second dielectric portions, respectively, forming firstand second piezoelectric layers on part of the first and second lowerelectrodes, respectively, and depositing first and second upperelectrodes on the piezoelectric layers and on part of the first andsecond dielectric portions not having the first and second lowerelectrodes, respectively.

The forming of the second substrate part may include selectivelydepositing a second dielectric layer on the second substrate formingfirst and second dielectric portions spaced apart from each other at adistance corresponding to a distance between the first and secondresonance parts and etching the second substrate without the seconddielectric layer to form the first and second cavities. The forming ofthe second substrate may further include forming a capacitor having twoconductive layers and a dielectric layer between the two conductivelayers, and forming a coil of another conductive layer on an upper partof the capacitor to form an inductor. The forming of the secondsubstrate part may further include depositing a first conductive layeron part of the second dielectric layer located between the first andsecond cavities, depositing a third dielectric layer on part of thefirst conductive layer and on the second dielectric layer, depositing asecond conductive layer on the third dielectric layer over the firstconductive layer and on part of the third dielectric layer not over thefirst conductive layer, coating an insulating film on part of the secondconductive layer and on part of the third dielectric layer, anddepositing a third conductive layer including forming a coil on exposedfirst and second conductive layers and on part of the insulating film.

The method may further include forming a pad by removing part of thefirst dielectric layer to expose lower and upper electrodes of the firstand second resonance parts. The securing may include bonding the firstand second substrate parts using adhesive bonding and/or eutecticbonding. The method may include forming at least two resonance parts onthe first substrate, and at least two cavities on the second substrate,a number resonance parts being equal to a number of cavities.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become readily apparent to those of skill in the art by describingin detail embodiments thereof with reference to the attached drawings,in which:

FIG. 1A illustrates a cross-section of a Bragg reflector type FBAR;

FIG. 1B illustrates a cross-section of a bulk micro-machining type FBAR;

FIG. 1C illustrates a cross-section of a surface micro-machining typeFBAR;

FIG. 2A illustrates a cross-section of a conventional duplexer on aprinted circuit board including the FBAR of FIG. 1B or 1C;

FIG. 2B illustrates a cross-section of a conventional duplexer includingthe FBAR of FIG. 1A;

FIG. 3 illustrates a cross-section of an air-gap type FBAR according toan embodiment of the present invention;

FIGS. 4A to 4J illustrate cross-sections at different stages offabrication of an air-gap type FBAR according to an embodiment of thepresent invention;

FIG. 5 illustrates a cross-section of a FBAR filter formed by connectingseveral FBARs according to the present invention;

FIG. 6 illustrates a cross-section of an air-gap type FBAR integratedwith a capacitor according to an embodiment of the present invention;

FIG. 7 illustrates a cross-section of a FBAR packaged using a firstsubstrate film according to another embodiment of the present invention;

FIG. 8 illustrates a cross-section of an FBAR packaged by bonding athird substrate having a separate cavity according to still anotherembodiment of the present invention;

FIG. 9 illustrates a cross-section of a duplexer according to thepresent invention;

FIGS. 10A to 10E illustrate cross-sections of a process of fabricatingresonance parts of an air-gap type FBAR used in a duplexer according tothe present invention;

FIGS. 11A to 11C illustrate cross-sections of a process of fabricatingair gaps for an air-gap type FBAR used in a duplexer according to thepresent invention;

FIGS. 12A to 12E illustrate cross-sections of a process of fabricatingan isolation part used in a duplexer according to an embodiment of thepresent invention;

FIGS. 13A to 13D illustrate cross-sections of a process of finallyfabricating a duplexer through a securing process according to thepresent invention;

FIG. 14 illustrates a cross-section of a duplexer fabricated using theisolation part illustrated in FIGS. 12A to 12E according to the presentinvention; and

FIG. 15 illustrates a cross-section of a duplexer using transmitter andreceiver filters in which several air-gap type FBARs are connectedtogether according to still another embodiment of the present invention.

DETAILED DESCRIPTION

Korean Patent Application No. 2003-24720 filed on Apr. 18, 2003 in theKorean Intellectual Property Office, and entitled “FILM BULK ACOUSTICRESONATOR FABRICATION METHOD USING SUBSTRATE BONDING AND FILM BULKACOUSTIC RESONATOR FABRICATED BY THE SAME,” and Korean PatentApplication No. 2003-49918 filed on Jul. 21, 2003 in the KoreanIntellectual Property Office, and entitled “ONE-CHIP DUPLEXERFABRICATION METHOD USING SUBSTRATE BONDING AND ONE-CHIP DUPLEXERFABRICATED BY THE SAME,” are incorporated herein by reference in theirentirety.

Hereinafter, an air-gap type FBAR, a duplexer and a fabricating methodthereof according to the present invention will be described in detailwith reference to the annexed drawings in which like reference numeralsrefer to like elements. The invention may, however, be embodied indifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the concept of the invention to those skilled in the art. In thedrawings, the thickness of layers and regions are exaggerated forclarity. It will also be understood that when a layer is referred to asbeing “on” another layer or substrate, it may be directly on the otherlayer or substrate, or intervening layers may also be present. Further,it will be understood that when a layer is referred to as being “under”another layer, it may be directly under, or one or more interveninglayers may also be present. In addition, it will also be understood thatwhen a layer is referred to as being “between” two layers, it may be theonly layer between the two layers, or one or more intervening layers mayalso be present.

FIG. 3 illustrates an air-gap type FBAR fabricated using a substratesecuring process. As shown in FIG. 3, a cavity 290 is formed on apredetermined part of a surface of a substrate 270, and a seconddielectric layer 260 a and 260 b is provided on the substrate 270 onopposite sides of the cavity 290. A laminated resonance part 300includes a first electrode 230, a second electrode 250 and apiezoelectric layer 240 located between the first and second electrodesand within the cavity 290. One end of the first electrode 230 of thelaminated resonance part 300 is in contact with one part 260 a of thesecond dielectric layer, and one end of the second electrode 250 is incontact with the other part 260 b of the second dielectric layer. Also,the first electrode 230 and the second electrode 250 are packaged by afirst dielectric layer 220, and parts of the first electrode 230 and thesecond electrode 250 are exposed by a via 280 a and 280 b formed byremoving part of the first dielectric layer 220.

When a voltage is applied to the first electrode 230 and the secondelectrode 250 through vias 280 a and 280 b, an electric field isgenerated between the two electrodes. This electric field producesmechanical motion in the piezoelectric layer 240 due to thepiezoelectric effect in the form of a bulk acoustic wave to generateresonance. The part that generates the resonance as described aboveincludes the first and second electrodes 230, 250, the piezoelectriclayer 240, and the first dielectric layer 220, and is referred to as theresonance part 300.

A method of fabricating an air-gap type FBAR having the structure ofFIG. 3 is illustrated in detail in FIGS. 4A to 4J. Generally, the methodincludes forming the laminated resonance part 300 on a first substrate210, forming the cavity 290 on the second substrate 270, and completingthe air-gap type FBAR including securing the second substrate 270 andthe first substrate 210. In detail, FIGS. 4A to 4D illustrate theprocess of fabricating the laminated resonance part, FIGS. 4E to 4Gillustrate the process of fabricating the cavity, and FIGS. 4H to 4Jillustrate the bonding and finishing process.

As shown in FIG. 4A, the first dielectric layer 220 is deposited on aseparate substrate (hereinafter referred to as “first substrate”) 210.The first dielectric layer 220 will serve to electrically insulate thefirst electrode 230 from the first substrate 210 and to facilitate thedeposition of the first electrode 230. The substrate 210 may be aninsulating material such as SiO₂ and Al₂O₂, but is not limited thereto.

A conductive material is selectively deposited, e.g., by depositing,patterning and removing in accordance with the pattern, on the firstdielectric layer 220 to form the first electrode 230, as shown in FIG.4B. The conductive material may be a metal, such as Al, W, Au, Pt, Ni,Ti, Cr, Pd and Mo.

A piezoelectric material is selectively deposited, e.g., by depositingand patterning, on the first electrode 230 to form the piezoelectriclayer 240, as shown in FIG. 4C. The piezoelectric layer 240 generatesthe bulk acoustic wave when an electric signal is applied thereto due tothe piezoelectric phenomenon. The piezoelectric material may be AlN orZnO, but is not limited thereto. The deposition may be performed usingRF magnetron sputtering or evaporation.

A second conductive material is selectively deposited, e.g., bydepositing and patterning, on the first dielectric layer 220 and thepiezoelectric layer 240 to form the second electrode 250, as shown inFIG. 4D. The second conductive material may be any of those noted abovefor the first electrode, and may be the same material as for the firstelectrode.

Through the above-described steps, the fabrication of the resonance part300 with respect to the first substrate 210 is completed.

Meanwhile, with respect to another separate substrate (hereinafterreferred to as “second substrate”), the cavity 290 for forming the airgap is created. The cavity 290 isolates the resonance part 300 from thesecond substrate 270, and thus prevents the acoustic wave generated fromthe piezoelectric layer 240 from being affected by the second substrate270. The cavity-formation may be performed as follows.

First, as shown in FIG. 4E, the second dielectric layer 260 is depositedon the second substrate 270. The deposition of the second dielectriclayer 260 may be performed in the same manner as the deposition of thefirst dielectric layer on the first substrate 210.

Then, the second dielectric layer 260 is patterned in a predeterminedform, as shown in FIG. 4F. That is, the portion of second dielectriclayer 260 that corresponds to where the cavity 290 will be formed on thesecond substrate 270, is removed.

Then, as shown in FIG. 4G, the cavity 290 is formed by removing, e.g.,etching, the substrate 270 part where the second dielectric layer 260was removed. The depth h of the cavity 290, labeled in FIG. 4J, is largeenough to isolate the resonance part 300 from the second substrate 270,and may be approximately in the range of 3 to 5 μm. As discussed inconnection with another embodiment below, a passive element and/or anactive element may be integrated with the cavity 290 and the depth h ofthe cavity can be adjusted accordingly. Through the above-describedsteps, the process for the second substrate 270 is completed.

Finally, in order to fabricate the air-gap type FBAR, the firstsubstrate 210 and the second substrate 270 are secured together.

First, the first substrate 210, in which the resonance part 300 isformed, is secured with the second substrate 270, in which the cavity290 is formed. The first and second electrodes 230, 250 of the resonancepart 300 of the first substrate 210 and the dielectric layer parts 260 aand 260 b of the second substrate 270 may be used as securing surfaces.Thus, the resonance part 300 on the first substrate 210 is locatedwithin the cavity 290 formed on the surface of the second substrate 270,as shown in FIG. 4H. In the present invention, since the FBAR isfabricated using securing, the air gap does not need to be formed usinga separate sacrificial layer and the attendant removal thereof.

The securing may include bonding the first and second substrates 210,270. Such bonding may include direct bonding that performs the bondingby applying heat, anodic bonding that performs the bonding by applyingvoltage, adhesive bonding using adhesive such as epoxy, eutectic bondingusing metal. Due to low-temperature processing available with adhesivebonding or eutectic bonding, these may be more practical than directbonding or anodic bonding, which include a high-temperature process.

After the completion of the securing, the first substrate 210 may beremoved, as shown in FIG. 4I. The removal of the first substrate 210 maybe performed through wet etching using KOH or TMAH (Tetra-MethylAmmonium Hydroxide), spin etching after lapping, or dry etching afterlapping. In order to reduce the stress of the element, dry etching afterlapping may be selected. After removing the first substrate part 210,the dielectric layer 220 remains to serve as packaging for the air-gaptype FBAR. Accordingly, the cost and effort of providing separatepackaging after the fabrication of the FBAR as in the conventionalmethod can be reduced.

Finally, the air-gap type FBAR is completed by patterning the firstdielectric layer 220 in order to form vias 280 a and 280 b for exposingthe first and second electrodes 230, 250 to form pads as shown in FIG.4J. The pads electrically connect the first and second electrodes 230,250 to external terminals, e.g., by wire, and vias 280 a and 280 b arethe paths for contacting the two terminals in the dielectric layer.

Accordingly, the air-gap type FBAR having a superior reflectioncharacteristic and a stable effective bandwidth can be robustlyfabricated through a simple process. Since a separate sacrificial layerremoving process is not required, the damage occurring during theremoval of the sacrificial layer can be prevented, and the limit on thesize of the area can be eliminated. Also, by forming the resonance partand the cavity on separate substrates, the fabricating process issimplified. Further, by creating packaging along with forming FBAR, thecost and effort to perform the separate packaging processes can bereduced.

Also, according to the FBAR of the present invention, the degree ofintegration of the element can be increased by separately forming apassive element and/or an active element on the substrate 270 having thecavity (i.e., the second substrate) and securing the resonance part 300thereto. The processing of the second substrate 270 may be compatiblewith the CMOS processing. The FBAR fabricated as above can be used tocreate a filter for wireless communication and a duplexer.

In one embodiment of the present invention as shown in FIG. 5, a filtercan be implemented by connecting FBARs shown in FIG. 3. When using FBARs100 as a filter as shown in FIG. 5, frequency tuning is required. Theresonance part 300 facilitates the frequency tuning by controlling thethickness of the first insulting layer 220 of the resonance part 300.The resonant frequency f₀ of the FBAR 100 is determined by the thicknessof the laminated resonance part 300 and the properties of itsconstituent materials. This can be expressed by an approximate equationof f₀=v/2 l. In the equation, v is a speed of a bulk acoustic wave inthe piezoelectric layer 240, and l is the thickness of the resonancepart 300. By controlling the thickness of the first dielectric layer220, the thickness/of the laminated resonance part 300 can be adjusted,allowing frequency tuning. The controlling of the thickness of the firstdielectric layer 220 may include removing a portion of the firstdielectric layer 220, e.g., by etching.

In another embodiment of the present invention, a metal layer 311 may bedeposited on a bottom surface of the cavity 290 before securing thefirst and second substrates, as shown in FIG. 6. In this case, thesecond electrode 250 of the resonance part 300 and the deposited metallayer 311 form a capacitor structure 310. When an electric field isapplied to the first and the second electrodes 230 and 250, theresonance is generated, and the resonance part 300 fluctuates, so thatthe second electrode 250 and the metal layer 311 serve as a variablecapacitor. In other words, since the distance d between the secondelectrode 250 and the metal layer 311 varies due to the fluctuating ofthe laminated resonance part 300, the capacitance C varies by anequation of C=∈(A/d), where ∈ is a dielectric constant, A is an area ofthe electrode part, and d is the distance between the electrodes. Thisvariable capacitor and the bulk acoustic resonator can be integratedinto one element.

In this embodiment of the present invention, a passive element and/or anactive element, separate from the FBAR, may also be integrated. That is,during the fabrication of the cavity 290 used as the air gap, anintegrated element can be fabricated before the securing process byproducing a passive element such as an inductor and a capacitor or anactive element such as a Complementary Metal Oxide Semiconductor (CMOS)and a diode. Since the processes for the first substrate 210 and thesecond substrate 270 can be performed separately, creation of such anintegrated element only needs to be compatible with the processing ofthe second substrate 270. Thus, for example, the CMOS can be fabricatedon the second substrate 270 using existing CMOS fabricating processes.

Meanwhile, in another embodiment of the present invention, rather thancompletely removing the first substrate 210 as shown in FIG. 4J, a morestable packaging may be realized by leaving a film of the firstsubstrate 210 of a predetermined thickness, as shown in FIG. 7. Thethickness of the first substrate film 210 may be within 3 μm and isdetermined in accordance with a desired degree of stabilization of theelement and a degree of deterioration of the resonance due to theaddition of the substrate film. As described above, the integration canbe performed on the PCB with packaging at a unit element level.

In another embodiment of the present invention shown in FIG. 8, a thirddielectric layer 410 is deposited on a separate third substrate 400, anda predetermined part of the third dielectric layer 410 is patterned andremoved. A cavity 420 is formed in the third substrate 400 where thethird dielectric layer 410 was removed. The third substrate 400 issecured to the first substrate film 210 of the FBAR shown in FIG. 7,using the part of the third dielectric layer 410 a and 410 b as asecuring surfaces. In the structure illustrated in FIG. 8, the thirdsubstrate 400 and the third dielectric layer 410 a and 410 b aredeposited in addition to the first substrate film 210. Thus, a morestabilized packaging can be achieved.

In the same manner, a more stabilized FBAR can be fabricated by bondingthe third substrate onto the FBAR according to the previous embodimentof the present invention in which the first substrate film 210 does notremain (not illustrated).

The duplexer shown in FIG. 9 includes a receiver filter, a transmitterfilter and an isolation part 700 formed between the receiver filter andthe transmitter filter on a substrate 610. The receiver filter and thetransmitter filter have the same structure, and hereinafter, theexplanation will be made with respect to the receiver filter.

Referring to FIG. 9, an air gap 630 b is formed by etching apredetermined part of the substrate 610, and a second dielectric layer620 is deposited around the air gap 630 b. The second dielectric layer620 serves to insulate the substrate 610 from upper and lower electrodes560 and 540. One side of the second dielectric layer 620 depositedaround the air gap 630 b is in contact with the lower electrode 540, andthe other side of the second dielectric layer 620 is in contact with theupper electrode 560. A piezoelectric layer 550 is provided between theupper and lower electrodes 560 and 540. When an electric field isapplied to the upper and lower electrodes 560 and 540, the piezoelectriclayer 550 produces a piezoelectric effect that converts the appliedelectric signal into a mechanical energy in the form of an acousticwave, and the air gap 630 b reflects the acoustic wave to generate aresonance phenomenon.

A first dielectric layer 520 is provided on an upper part of the upperand lower electrodes 560 and 540. Part of the first dielectric layer 520is removed to expose parts of the upper and lower electrodes 560 and540, so that pads 810 are formed. The pads 810 connect the upper andlower electrodes 560 and 540 to external electrodes. The air-gap typeFBAR having the above-described structure serves as a kind of band-passfilter.

Meanwhile, a transmitter filter having the same structure as thereceiver filter is formed over another air gap 630 b. In fabricating thereceiver filter and the transmitter filter, by adjusting the thicknessof the upper and lower electrodes 560 and 540 and the thickness of thefirst dielectric layer 520, the resonance frequency can be changed. Thetransmitter and receiver filters pass only signals having frequencies intheir respective resonance frequency bands, making it possible totransmit/receive the signals through one antenna.

Since most systems use similar transmitted/received frequencies, aninterference phenomenon may be generated between the transmitter andreceiver filters, producing noise during communication. In order toprevent the interference phenomenon, the transmitter and receiverfilters are isolated from each other. For this, the isolation part 700is formed between the transmitter and receiver filters.

The isolation part 700 may include a structure in which a capacitor andan inductor are provided in order. The isolation part 700 serves as aphase shifter for shifting the phases of the frequencies input to thetransmitter and receiver. For example, a phase difference of 90° betweenthe frequencies may be introduced. Then, if the transmitted signal flowsto the receiver, it is reflected because of the phase difference,thereby preventing interference.

Meanwhile, FIGS. 10A to 10E, 11A to 11C, 12A to 12E, and 13A to 13Dillustrate cross-sections during a process of fabricating a single-chipduplexer according to the present invention. FIGS. 12A to 12E show theprocess of fabricating the isolation part having a specified structureaccording to an embodiment of the present invention, but the isolationpart may have a structure different from that illustrated in FIG. 12.

FIGS. 10A to 10E illustrate cross-section of the process of fabricatingthe resonance parts of an air-gap type FBAR, which serve as the receiverfilter and the transmitter filter of a duplexer, on the first substrateaccording to the present invention. In this example, two resonance partsare fabricated, but several resonance parts may be fabricated. Forexample, the filter may be made by connecting several air-gap type FBARsas disclosed below in connection with FIG. 15. In the followingdescription, the first substrate 510 in which the laminated resonanceparts are fabricated is called a first substrate part 500 used in thesecuring process of FIGS. 13A–13D.

First, a first dielectric layer 520 is deposited on the first substrate510 as shown in FIG. 10A. Then, part of the first dielectric layer 520is patterned and removed, as shown in FIG. 10B. The part from which thefirst dielectric layer 520 is removed corresponds to a part in which theisolation part 700 to be formed. Since the two air-gap type FBARs, whichserve as the transmitter and receiver filters, are fabricated using thesame method and have the same structure, the description is providedonly with respect to the fabrication of one resonance part.

In FIG. 10C, a conductive material is deposited on upper parts of thefirst dielectric layer 520 separated as above to form the lowerelectrode 540. The material and the role of the lower electrode 540 arethe same as described above. One end of the lower electrode 540 may bealigned with one end of the first dielectric layer. Thus, the lowerelectrode 540 can strongly support the resonance part.

Thereafter, a piezoelectric layer 550 is deposited on a predeterminedpart of the lower electrode 540, as shown in FIG. 10D. Then, as shown inFIG. 10E, an upper electrode 560 is deposited on the part of the firstdielectric layer 520 where the lower electrode 540 is not deposited andon the upper part of the piezoelectric layer 550. In the same method,another resonance part can be fabricated on the opposite part of thefirst dielectric layer 520. Through the above-described processes, thefirst substrate part 500 is completely fabricated.

Meanwhile, FIG. 11A to 11C show the process of fabricating the secondsubstrate part by forming air gaps or cavities and the isolation part700 on a separate substrate. In the following description, the secondsubstrate 610 in which the air gaps and the isolation part 700 arefabricated is called a second substrate part 600 used in the securing ofFIGS. 13A–13D.

First, the second dielectric layer 620 is deposited on the secondsubstrate 610 as shown in FIG. 11A. Then, the parts of the seconddielectric layer part 620, on which the air gaps 630 b are to be formed,are removed as shown in FIG. 11B. Since the number of the air gaps 630 bshould be equal to the number of laminated resonance parts on the firstsubstrate, the etching of the second dielectric layer 620 is performedaccordingly.

Thereafter, the air gaps 630 b (or cavities) are formed by removing,e.g., by etching, some of the substrate of the part 630 a from which thesecond dielectric layer 620 has been removed, as shown in FIG. 11C. Thedepth of the air gap 630 b is large enough to isolate the laminatedresonance part fabricated on the first substrate from the secondsubstrate 610. When two resonance parts are fabricated on the firstsubstrate, two air gaps 630 b are formed. If more than two FBARs are tobe employed, the number of the resonance parts and the air gaps isadjusted accordingly.

After the air gaps 630 b (or cavities) are formed, the isolation part700 may be fabricated as shown in FIGS. 12A to 12E. The isolation part700 may be fabricated by forming a capacitor having two conductivelayers and a dielectric layer located between the two conductive layersand by implementing an inductor having a conductive coil.

A first conductive layer 640 is deposited on an upper part of the seconddielectric layer 620 between the two air gaps 630 b formed on the secondsubstrate 610, as shown in FIG. 12A. The first conductive layer 640 maybe a metal, e.g., Au, Cr, and may be formed by electroplating.

A third dielectric layer 650 is then selectively deposited on the firstconductive layer 640 and on the upper part of the second dielectriclayer 620, as shown in FIG. 12B. The material of the third dielectriclayer 650 may be Si₃N₄. The selective provision of the third dielectriclayer 650 may include depositing dielectric material using PECVD (PlasmaEnhanced Chemical Vapor Deposition) over the entire structure, and thenremoving a predetermined part of the third dielectric layer 650 usingreactive-ion etching, thereby exposing parts of the first conductivelayer 640.

Then, a second conductive layer 660 is deposited on predetermined partsof the third dielectric layer 650, as shown in FIG. 12C. The secondconductive layer 660 may be made of the same material as the firstconductive layer 640 and deposited using the same method such aselectroplating.

An insulating material, e.g., an organic insulating material (BCB), isprovided over the structure show in FIG. 12C. The insulating materialmay have a low dielectric constant k and a thickness of about 8 μm. Partof the insulating material is removed to expose a predetermined part ofthe second conductive layer 660 and a predetermined part of the firstmetal layer 640, as shown in FIG. 12D, thereby forming an insulatingfilm. The insulating film 670 serves as a protective layer forprotecting the conductive layers 640, 660 and the dielectric layer 650.

A third conductive layer 680 is provided on predetermined parts of theexposed first conductive layer 640, second conductive layer 660 andorganic insulating film 670, as shown in FIG. 12E. The third conductivelayer 680 may be a coil, and serves as an inductor. Generally, the thirdconductive layer 680 may be a metal, e.g., Cu, and may be provided byelectroplating. The third conductive layer 680 may be made into the coilby forming a seed layer, forming photoresist film patterns on the seedlayer, electroplating a coil material between the photoresist filmpatterns, and removing the photoresist film patterns, leaving the coil.

After forming of the third conductive layer 680 in the form of a coil,the process of fabricating the isolation part 700, and thus the secondsubstrate part 600, is finished.

FIGS. 13A to 13D illustrate cross-section of the process of securing thefirst substrate part 500 fabricated through the process as illustratedin FIGS. 10A to 10E to the second substrate part 600 fabricated throughthe process as illustrated in FIGS. 11A to 11C and 12A to 12E.

FIG. 13A shows the alignment of the first substrate part 500 and thesecond substrate part 600. In particular, the parts 500, 600 are alignedso that the resonance parts of the first substrate part 500 are alignedwith the two air gaps 630 b or cavities of the second substrate part600, while the isolation part 700 of the second substrate part 600 isaligned with the part 530 of the first substrate part 500 on which thereis no first dielectric layer 520. The securing may be performed usingany of the bonding techniques described above, again with adhesivebonding or the eutectic bonding providing advantages. Since the FBARsare fabricated through the securing of two substrates, the use of aseparate sacrificial layer and removal thereof as in the conventionalmethod to form the air gap is not needed.

The aligned substrate parts 500, 600 are brought into contact andsecured, as shown in FIG. 13B. The substrate 510 of the first substratepart 500 located on the upper part of the duplexer is then removed, asshown in FIG. 13C.

Then, parts of the first dielectric layer 520 under which the lowerelectrodes and the upper electrodes exist are removed to provide pads810, as shown in FIG. 13D. As described above, the pads supply anelectric field from an external terminal. Thus, a receiver filter 800 a,a transmitter filter 800 b and an isolation part 700, as shown in FIG.14, are formed on one substrate to complete a single-chip duplexer.

Since the receiver filter 800 a and the transmitter filter 800 b used inthe duplexer serve as band-pass filters having different resonancefrequencies, a frequency tuning process is required. In the presentinvention, each of the two laminated resonance parts includes the lowerelectrode 540, the piezoelectric layer 550, the upper electrode 560, andthe first dielectric layer 520, shown in FIGS. 9 and 14. Frequencytuning can be readily performed by removing part of the first dielectriclayer 520 of the resonance part. The frequency tuning method andprincipal are as described above.

As shown in FIG. 15, the pass frequency band of the transmitter/receivercan be adjusted by connecting the two FBARs together. In FIG. 15, theduplexer is fabricated using the isolation parts according to anembodiment of the present invention.

In addition to the above, the CMOS can be integrated onto the duplexer.Since the processes for the first substrate part 500 and the secondsubstrate part 600 are separately performed, the duplexer integratedwith the CMOS can be fabricated by forming the CMOS using existing CMOSfabricating processes, completing the second substrate part 600 byforming the air gaps and the isolation part on the second substrate, andthen securing the first and second substrate parts. In this case, theexisting CMOS fabricating equipment and process can be used as is toachieve the compatibility.

As described above, according to the present invention, a small,lightweight duplexer can be fabricated through a simple substratebonding process, and thus the damage of the substrate can be reduced.Also, since the transmitter and receiver filters and the isolation partare fabricated on separate substrates, the complexity of process causedby depositing different materials on one substrate can be reduced,simplifying the whole process. Also, since the connection betweenelements is performed on the substrate, in contrast to the conventionalmethod, the parasitic component is reduced, improving the performance ofthe duplexer.

While embodiments of the present invention have been disclosed hereinand, although specific terms are employed, they are used and are to beinterpreted in a generic and descriptive sense only and not for purposeof limitation. Accordingly, it will be understood by those of ordinaryskill in the art that various changes in form and details may be madewithout departing from the spirit and scope of the present invention asset forth in the following claims.

1. An air-gap type film bulk acoustic resonator (FBAR), comprising: asubstrate having a cavity in an upper surface of the substrate; a firstdielectric layer on the upper surface of the substrate around thecavity, the first dielectric layer at least partially defining anentrance to and exposing a surface of the cavity; and a resonance partincluding: a first electrode on part of the first dielectric layer, asecond electrode on the first dielectric layer, exclusive of the firstelectrode, and a piezoelectric layer between the first and secondelectrodes, wherein at least a portion of the piezoelectric layerextends along a same plane as the first dielectric layer that issubstantially parallel to the substrate.
 2. The FBAR as claimed in claim1, further comprising a conductive layer on a bottom surface of thecavity.
 3. The FBAR as claimed in claim 1, further comprising an elementintegrated onto a bottom surface of the cavity.
 4. The FBAR as claimedin claim 3, wherein the element includes at least one of a passiveelement and an active element.
 5. The FBAR as claimed in claim 1,wherein the resonance part is on a second substrate.
 6. The FBAR asclaimed in claim 5, further comprising a second dielectric layer betweenthe resonance part and the substrate, the second dielectric layer beingon the second substrate.
 7. The FBAR as claimed in claim 1, furthercomprising a second dielectric layer on the resonance part.
 8. The FBARas claimed in claim 7, further comprising a substrate film of apredetermined thickness on the second dielectric layer.
 9. The FBAR asclaimed in claim 8, further comprising: a third dielectric layer on aportion of a surface of the substrate film; and a third substratecontacting the third dielectric layer, the third substrate including acavity formed apart from where the third substrate contacts the thirddielectric layer.
 10. The FBAR as claimed in claim 1, further comprisinga via exposing a pad for providing electrical contact with one of thefirst and second electrodes.
 11. A single-chip duplexer having anair-gap type film bulk acoustic resonator (FBAR) filter, comprising: asubstrate having first and second cavities formed on an upper surface ofthe substrate; a first dielectric layer deposited on the upper surfaceof the substrate around the first and second cavities; a first air-gaptype FBAR including a first resonance part over the first cavity; asecond air-gap type FBAR including a second resonance part over thesecond cavity; and an isolation part between the first air-gap type FBARand the second air-gap type FBAR, wherein each of the first and secondresonance parts includes: a lower electrode; an upper electrode; and apiezoelectric layer formed between the lower electrode and the upperelectrode over each of the first and second cavities, wherein at least aportion of the piezoelectric layer extends along a same plane as thefirst dielectric layer that is substantially parallel to the substrate.12. The duplexer as claimed in claim 11, wherein: each of the lowerelectrodes is on an upper surface of the first dielectric layer on oneside of the respective first and second cavity and extends over therespective one of the first and second cavities; and each of the upperelectrodes is on the upper surface of the first dielectric layer on anopposite side of the respective one of the first and second cavities andextends over the respective one of the first and second cavities. 13.The duplexer as claimed in claim 11, wherein the first air-gap type FBARserves as a transmitter filter and the second air-gap type FBAR servesas a receiver filter.
 14. The duplexer as claimed in claim 13, whereinthe transmitter filter and the receiver filter are implemented byconnecting more than one air-gap type FBARs.
 15. The duplexer as claimedin claim 13, wherein the isolation part includes a capacitor and aninductor, and introduces a phase difference between frequencies ofsignals input to the transmitter filter and the receiver filter.
 16. Theduplexer as claimed in claim 11, wherein the isolation part includes: asecond dielectric layer on the substrate; a first conductive layer onpart of the upper surface of the second dielectric layer; a thirddielectric layer on part of the first conductive layer and on part ofthe upper surface of the second dielectric layer; a second conductivelayer on part of the third dielectric layer over the first conductivelayer and on part of the third dielectric layer below which the firstconductive layer is not present; an insulating film on part of thesecond conductive layer and on an upper part of the third dielectriclayer; and a conductive coil on an upper part of the insulating film andon upper parts of exposed first and second conductive layers.
 17. Theduplexer as claimed in claim 11, further comprising: first and seconddielectric portions spaced apart from each other at a distancecorresponding to a distance between the first and second resonanceparts.
 18. The duplexer as claimed in claim 11, wherein the isolationpart comprises: a capacitor; and an inductor on an upper part of thecapacitor.
 19. The duplexer as claimed in claim 11, further comprising avia exposing a pad for providing electrical contact with the lower andupper electrodes of the first and second resonance parts.
 20. Theduplexer as claimed in claim 11, wherein the first and second resonanceparts are on a second substrate.